There is a widespread need for inspection data for electronic parts in a manufacturing environment. One common inspection method uses a video camera to acquire two-dimensional images of a device-under-test. Current systems have problems. The problems include the inability of getting separated images of portions of the electronic part. To inspect leads on a part, the leads are lighted from the front. One row of leads, solder balls, or pins, for example, along an edge of the part, are lighted from the front and focused on, so that the row of leads on the opposite edge are out of focus thus allowing geometric measurement of the nearby leads. When electrical leads or other shiny surfaces are viewed using front lighting specular reflections result. Portions of the part causing specular reflections generally can not be measured or handled by an optical system. Elimination of specular reflections requires backlighting of the parts. In current inspection systems, backlighting has a problem since the various features to be viewed are not separated. For example, viewing a first row of leads along an edge also shows another row of leads on an opposite edge. The result is that the information sought, such as co-planarity and other critical parameters may not be accurately obtained since the features behind a critical portion of the object or device under test can not be viewed separately. In other words, the data collected on backlit parts may be bad since another portion of the device under test may introduce error in the measurement of the part.
U.S. Pat. No. 6,141,040 entitled “Measurement and Inspection of Leads on Integrated Circuit Packages” and issued to Toh discusses an arrangement of optics, cameras and an image processor for capturing images of lead tips of object fields resulting in accurate three dimensional positions of all the leads on a integrated circuit such as a Quad Flat Package (QFP). The system includes a telecentric lens attached to a camera working with an arrangement of mirrors and lighting. The telecentric lens and mirror optical layout splits the acquired image into 2 orthogonal viewing fields of the same lead tips of the QFP. The QFP is placed flat on a pedestal, and for any given side of the QFP, the first field views the lead tips from the front. The second field views the lead tips from the bottom of the IC package. Lead tip images are acquired by a lighting arrangement that casts illumination on the lead tips only. Electronic processing techniques are used to compute the geometry of the leads such as global co-planarity, lead standoff and inspection of other lead defects. This invention only provides views of leads on one side of a package. In addition, the leads are illuminated from the side facing the camera rather than back lighting the leads.
U.S. Pat. No. 6,243,164 entitled “Method and System for Determining Co-planarity” and issued to Baldwin, et al. discloses another system. The co-planarity of leads of an integrated circuit (IC) in a surface-mount technology package (SMT) can be determined by means of a plurality of views without the use of a conventional pedestal, without the use of an associated Z-axis actuator, and without the associated delays required to deploy such a Z-axis actuator. In the invention, three leads of SMT package are arbitrarily selected to define a virtual reference plane in a first or virtual coordinate system, and the positions of the unselected leads are measured with reference to the virtual reference plane. For convenience, the virtual reference plane can be defined as Z=0 and may have height coordinates in Z that are negative or positive with respect to the virtual reference plane. The virtual coordinates are analyzed, and three leads having the lowest Z coordinates are determined to define a virtual sitting plane. For convenience, the virtual sitting plane can be defined as Z=0 in a second or real coordinate system. A mathematical transformation that relates the first coordinate system to the second coordinate system is determined, and the coordinates for each lead of SMT package are subsequently transformed from the first coordinate system to the second coordinate system. In the second coordinate system, each Z coordinate directly corresponds to the lead standoff value that largely determines the acceptability of the inspected SMT package. A variety of techniques are optionally employed to determine whether SMT package is bi-stable.
U.S. Pat. No. 4,959,898 entitled “Surface Mount Machine with Lead Coplanarity Verifier” and issued to Landman, et al. discloses an apparatus for performing a non-contact three-dimensional inspection of a surface-mount component prior to placement on a printed circuit board. Specifically, an arrangement to ensure acceptable alignment (i.e. co-planarity) of all component leads in the XZ or YZ plane, where XY is the plane of the component. The apparatus is embodied within a conventional pick and place machine and performs critical, in-process, lead co-planarity inspection. U.S. Pat. No. 4,959,898 also has problems. The views of each of the edges including leads are not separated from one another. There is no divider and therefore there is no separation or blocking off of the view of the leads on the opposite edge of the surface mount component from being shown in a view of the nearby edge.
To overcome the problems stated above as well as other problems, there is a need for an improved machine-vision system that can view sub portions of a device under test using backlighting. There is a further need for a machine vision system that minimizes the problems associated with specular reflections off of shiny surfaces of a device under test. There is a further need for a machine vision system that can accurately measure selected portions of a device under test. There is still a further need for a device that can isolate selected portions of a device under test to assure the accuracy of measurements made on the part. In addition, there is a need for a device that uses a single camera to produce an image with all the desired views. There is also a need for a mechanical system that allows for automated, high-speed, two-dimensional inspection of objects or devices under test.